In the past, there have been many mechanisms using counter-rotating crankshafts geared together, and two or more connecting rods attached directly to a piston. These mechanisms have been employed in internal combustion engines or fluid pumps. The advantages are many: (1) the elimination of the side thrust on the piston which is possible with two or more opposed connecting rods; (2) to permit a large offset of the crankshaft rotational axis with respect to the axis of reciprocation and thereby achieve useful modifications of conventional piston motion without very high thrust loads on the piston; (3) to achieve a piston motion which may compliment and thereby improve the efficiency of a given thermodynamic or fluid cycle; and (4) to achieve a better balance which is possible with phased-together, counter-rotating crankshafts.
The modern necessity for lightweight, high powered, and more efficient engines has required smaller displacement, more compact engines which operate at higher speeds. Some dual, counter-rotating crankshaft engines have the advantages described above; but cannot be operated at very high speeds, cannot be made compact in important dimensions, and do not afford a very wide choice of functional and structural geometry.
The altered piston timing engine patent of Bertin R. Chabot, Jr. (U.S. Pat. No. 4,945,866) recognizes and documents the benefits of an engine which has an offset between the axis of rotation of the crankshaft and the centerline of the piston reciprocation. This proposal, however, makes no attempt to eliminate the higher thrust which acts upon the piston as a consequence of the offset and resulting higher maximum connecting rod angle. This engine uses a conventional single-rotating crankshaft and connecting rod and thereby eliminates the possibility to obtain the advantages available with two counter-rotating crankshafts.
U.S. Pat. No. 2,362,838 issued to M. Mallory on Nov. 14, 1944, entitled "Internal-Combustion Engine", discloses a single-crankshaft motor which employs a connecting rod with a displaced shaft having a straight lateral profile and one radius at the base of one side where the connecting rod joins the crankshaft journal. In this engine, the piston cylinder is offset and includes a central cylinder wall which is located directly above the axis of rotation of the crankshaft. The base of this central cylinder wall is cut away to permit passage of the connecting rods which are disposed on the crankshaft side-by-side, moving in separate parallel planes.
U.S. Pat. No. 4,791,787 issued to Paul et al, entitled "Regenerative Thermal Engine", discloses a twin crankshaft engine having two connecting rods affixed to a single piston. Because it utilizes conventional straight connecting rods, this motor must provide an extremely large bore for its piston stroke and therefore is highly impractical for high-speed operation because of the mass of the large piston.
The multi-connecting rod engine of Ian R. Hammerton (U.S. Pat. No. 5,435,232) utilizes two phased-together, spaced-apart, counter-rotating crankshafts and two or more connecting rods which are connected to a single reciprocating piston. Construction of this machine with overlapped crankshafts is complex and costly, and cannot be made compact. In the case where this machine employs three or more connecting rods, either the piston must be made very large to accommodate the attachments of the connecting rods, or the spaced-apart connecting rod attachments to the piston must be displaced toward each other to fit in the available space. As a result, transverse thrust forces are developed at both ends of these connecting rods, and they must be made heavier to support bending loads in the lateral direction. Where this device employs only two connecting rods, the transverse spacing of these connecting rods will create a moment (torque) on the piston which acts around the centerline of the piston and cylinder and will tend to twist the piston in opposite senses as each stroke of the piston is completed. These conditions prevent efficient operation at very high speeds.
Prior mechanisms using counter-rotating, phased-together crankshafts do not provide a mechanism which incorporates special characteristics to provide specific advantages for two-wheeled vehicles. There is therefore a need in the art for a device which solves these problems and which provides an advantageous powerplant for a two-wheeled vehicle.